The invention relates to closure covers for a tank under internal pressure, with a cover body which can be fixed in a tank neck by means of rotation, and with a cover which is provided with a handle and is operatively connected to the cover body. It also relates in particular to a closure cover for a motor vehicle fuel tank under slight excess pressure.
US 2001/0047995 describes a tank cover which closes off the filler neck of a motor vehicle fuel tank in a vapor tight manner; this being intended to minimize the emission of fuel vapors. Nevertheless, new tank covers are provided with pressure control valves that must close reliably and leaktightly and open only extremely infrequently.
For reasons connected with the engine, attention has recently focused on maintaining a slight excess pressure within the tank. To prevent fuel vapors from escaping, the tank must not be opened while the slight excess pressure provided for normal operation prevails therein, i.e. while the pressure is above a first threshold value. During normal operation, attention has to be paid to good sealing. This applies also to the pressure control valve, which opens at a second, higher, threshold value and must be arranged and designed accordingly.